Sen. Frank Lautenberg, D-N.J. walks to the Senate floor from a Democratic caucus meeting on Capitol Hill in Washington, Thursday, Feb. 14, 2013. Lautenberg, 89, has decided not to seek re-election on order to clear the way for Democratic Newark Mayor Cory Booker to assume the spot. (AP Photo/J. Scott Applewhite)— AP

Sen. Frank Lautenberg, D-N.J. walks to the Senate floor from a Democratic caucus meeting on Capitol Hill in Washington, Thursday, Feb. 14, 2013. Lautenberg, 89, has decided not to seek re-election on order to clear the way for Democratic Newark Mayor Cory Booker to assume the spot. (AP Photo/J. Scott Applewhite)
/ AP

PATERSON, N.J. 
A day after announcing he would not seek a sixth term, Democratic U.S. Sen. Frank Lautenberg said he will spend his last two years in office fighting for the same causes he always has, including tougher gun control laws.

"I am not announcing a retirement," Lautenberg said in a speech in his hometown of Paterson. "I am announcing today I will be continuing on my mission to do the right thing wherever I can."

Lautenberg, at 89 the oldest member of the Senate, made no mention of any Democrat who he might like to succeed him.

His revelation Thursday he would not seek re-election in 2014 cleared the way for Newark Mayor Cory Booker to accelerate his campaign for the U.S. Senate seat. Booker's announcement in December that he intended to run for the seat had angered Lautenberg, who had wanted the Democratic mayor to hold off until he decided his plans.

Lautenberg also did not say why he decided to retire when his term ends in 2015. He joked at least twice about possibly staying on. "Too late to change my mind?" he asked with a smile.

Asked after his speech who he would like to see take his seat in the Senate, he joked: "Well I'd like to have my wife do it, but she's busy."

Asked why he decided to call it quits in 2015, he said: "Nothing. I think the time with family. My children, my daughters, my grandchildren live all over the country and I want to spend more time with them."

On the issues he will focus on, the liberal Democrat cited gun control first. "We are tired of assaults on our children," he said.

Early public opinion polls had showed Booker as a strong favorite over the incumbent to keep the seat in Democratic hands, but Booker's nascent campaign had been largely on hold until Lautenberg made a decision. Other Democrats, including Rep. Frank Pallone, are also mulling runs.

No Republican has publicly expressed interest in the seat, but a spokesman for the national party viewed Gov. Chris Christie's success in New Jersey as "a hopeful sign" for the GOP's chances even though New Jersey voters haven't sent a Republican to the Senate in 40 years.

Booker created a federal fundraising account allowing him to raise money for the campaign. In doing so, the two-term mayor of New Jersey's largest city dashed hopes that he would challenge Christie in a race for governor that would have pitted two rising national stars against one another.

Though Booker's relationship with Lautenberg has been nettlesome, he issued a statement praising the senator.

"Sen. Frank Lautenberg has been a champion for the people of New Jersey for decades and his legacy of service will improve the lives of all Americans for years to come," Booker said.

President Obama also lauded the reliably liberal senator.

"Throughout his time in the Senate, Frank has fought tirelessly for workers, veterans, members of our military and their families, and immigrants, and he continues to make extraordinary contributions to our nation's safety, and the health and welfare of our citizens," Obama said.